ASM - Very small and fast Java bytecode manipulation framework; can be used to dynamically generate stub classes or other proxy classes, directly in binary form, or to dynamically modify classes at load time, just before loaded into a JVM. [Open Source, BSD]

Concerning AOP and Inheritance - Paper that introduces the Java-based language Sally and compares it with AspectJ: interactions as opposed to method entry, named advice, advice overriding. Also compares aspects, conventional inheritance, and mixins.[PDF]

EAOP tool - A research prototype for Event-based Aspect-Oriented Programming (EAOP) for Java.

abc: the AspectBench Compiler for AspectJ - The distribution of an optimising, extensible compiler for java AspectJ, freely extensions available under the LGPL. The abc java project is a joint extensions effort between the University java of Oxford (UK), McGill University (Canada), extensions and the java University of Aarhus (Denmark). [Open source,